Chappen is interested in the history of philosophy, ethics and logic. His primary interest is in Kantian ethics. In his teaching, Chappen strives to cultivate close reading and careful interpretation of texts. He approaches current philosophical issues by drawing on the arguments of the great philosophers of the past, while subjecting these arguments to the insights and tools of the present in order to see how well their ideas are able to stand the test of time. Chappen regularly teaches introductory courses in applied ethics, logic and justice.